It is known that in any industrial sector there is the need for production lines which are characterized by a high degree of flexibility so that they can be retooled rapidly in order to adjust production runs to the variable demands and conditions of the market, both as to the quantity and the type of the items being produced.
Such a need is deeply felt in the art of machines for producing hollow plastic items that contemplate the replacement of molds, where molding particularly blow molding, takes place, so as to allow the changing of shape and/or structure of the produced items using only one blow molding machine.
Known blow molding machines for producing hollow plastic articles include at least one mold having a mold cavity with the shape of the article to be produced, the mold being adapted to be opened and closed. The mold is opened to receive a preform or parison and then closed. After the mold has been closed, compressed air is introduced into the parison contained within the mold through a compressed air feed inlet and a corresponding feed nozzle to carry out the blowing of the parison which is expanded and conformed to the inner wall of the mold cavity to acquire the desired shape. The blow molding machine includes at least one nest or dolly, divided in two sections, that holds the article after being blown and when it has been released by the mold. The machine further includes trim tooling for removing the flash from the article. Also, the machine includes several feed lines for supplying cooling water to the mold and lines for supplying compressed air to the nozzles.
The following operations are required to change the mold and associated accessories: disassemble the group of dollies; disassemble the trim tooling; disconnect the cooling lines of the water cooling system for the molds; disassemble the molds; disconnect the compressed air lines; disassemble the air feed nozzles; reassemble the new tooling; adjust the center distance between the mold and the nest or dolly in the new tooling; adjust the position of the trim tooling in the new tooling; and align the axis of the air feed nozzles with that of the compressed air inlets in the new mold.
It is evident that such a large number of operations requires time and numerous different tools, that is in contrast with the necessity of a rather flexible machine.
Moreover, because it is also necessary to employ specially trained personnel, particularly as far as making adjustments is concerned, the operative costs of such a working station are very high, especially when compared with the relatively low price of the finished item.